The excited states of carcinogenic polycycloaromatics are involved in the irreversible binding to the DNA in UV carcinogenesis. Coumarins, particularly furocoumarins, also show similar photochemical and photobiological effects. Many furocoumarins are responsible for skin erythema and related skin diseases. In addition, aflatoxins, which contain the coumarin chromophore, are potent carcinogens. Synthetic analogs possessing the unique photoreactivity for cross-linking the DNA strands, benzodipyrones, will be examined with respect to their photobiological reactivity. The specific objective of this proposal is, therefore, to elucidate the chemical mechanisms of interactions between DNA (and tRNA) and skin-sensitizing and -carcinogenic coumaryl compounds under the influence of light. Information concerning the mode of interactions will be obtained, and biological effects of these interactions (intercalation, photoaddition, and cross-linking) will be ascertained in terms of specific effects of these compounds on Bacillus subtilis. BIBLIOGRAPHIC REFERENCES: J. N. Marx, P. S. Song and P. K. Chui, Synthesis of cis- and transbenzodipyrones, potential photochemical DNA crosslinking agents, J. Heterocyclic Chem., 12, 417 (1975). P. S. Song, C. A. Chin, I. Yamazaki and H. Baba, Electronic structure and photoreactivity of the triplet states of skin-sensitizing psoralens, Internat. J. Quantum Chem., Suppl. Quantum Biol. Pharmacol., (1975), in press.